Marine waterjets have many benefits for propulsion of marine vessels, such as higher safety, higher efficiency, shallow draft and outstanding maneuverability. However, a disadvantage of conventional waterjet systems is the large amount of space taken up by the motor and the gearbox that are typically placed in front of the waterjet inside the vessel. The motor drives the waterjet via a transmission that adapts the rotational speed of the motor to that of the waterjet. A drive shaft with flexible couplings at each end, a shaft tube, and a water seal connect the transmission to the impeller of the waterjet. The shaft and shaft tube pass through the waterjet intake duct, obstructing the water flow in the intake duct to the impeller, lowering the efficiency of the waterjet. U.S. Pat. No. 5,421,753 shows such a drive arrangement. The placement of the intake duct inside the vessel near the transom requires special tools and skills on the part of the waterjet manufacturer, the vessel manufacturer or retrofitter.
In conventional waterjet systems, the cleaning of the intake grid that protects the waterjet from ingesting debris is often an extremely arduous task simply because it is difficult to reach the intake grid with the waterjet in its permanently-installed position in the vessel.
Conventional outboard motors are generally heavy, noisy, and costly. Much of the cost is associated with the power transmission linkage between the power head and the propeller, and the components of this linkage are of necessity metallic.
Often, users of conventional outboard motors also purchase an electric trolling motor for both convenience and trolling performance. This combination, viewed by most fisherman as a necessity, adds further cost for the user.
In recent years, battery technology has developed rapidly, to the point where the stored energy densities of some batteries make electric propulsion of marine vessels a possibility. Further, advances in semiconductor switching technology enable numerous electric motor developments that would not have been possible in the past.